1. Field of the Invention
The present invention relates to the field of computer graphics, and more particularly, to a method and apparatus for efficiently displaying pixels stored in a multi-format pixel frame buffer on a computer display monitor.
2. Art Background
Computer systems perform a variety of functions including data acquisition, data processing and display of graphical images. The ability to integrate different external sources to one central processing unit generates a plurality of applications. For example, computers find applications in telecommunication systems where the display monitor provides a graphical display for input messages to an operator, and a man to machine interface provides a means for the operator to generate output messages. Computers also provide a variety of applications in the field of publishing. For example, data bases are generated from external sources, such as imaging scanners or other computer generated data. The data bases from the external sources are input to the computer resulting in a plurality of data formats. In addition, computers have applications for multi-media production which is the integration of several audio and video production units into a single controllable unit. Multi-media projects cover many communication media types, including printed materials, audio programs, television shows, feature films and many others.
As illustrated in the above examples, a computer, configured for data integrated applications, receives data in a plurality of data formats. In order for the operator of the computer to view the data or related information on a display monitor, the data require conversion to a format compatible with the display monitor. For example, a operator may program a computer to display graphical images depicting a spreadsheet on the display monitor, and at the same time, desire to create a display window for a conference call. Although the computer system provides a means to integrate the video signal into the computer environment for the conference call, the video signal comprises a different picture element or pixel format. Furthermore, if the operator desires to integrate several sources each with a different format, the problem is increased.
Generally, in computer graphic systems, a frame buffer is implemented in conjunction with a computer display monitor. The frame buffer contains pixels in a digitized form for display on the corresponding display monitor. The pixel data is arranged in the frame buffer in rows and columns that correspond to rows and columns on the display monitor. To display a graphical image on the display monitor, the pixel data is transferred from the frame buffer and converted to an analog signal by a digital to analog converter (DAC). In a system having multi-format pixel data, each pixel format must be converted to a standard format for the video monitor before conversion to the analog signal. The analog signal is input to the display monitor to generate the graphical image.
Referring to FIG. 1, a prior art method for displaying multi-format pixels on a computer display monitor is illustrated. The multi-format pixel display system comprises a frame buffer for each pixel format type. For the graphics display system illustrated in FIG. 1, frame buffer 12 contains RGB index pixel data, frame buffer 14 contains luminance/chrominance or YUV pixel data, and frame buffer 13 contains RGB value pixel data. In order to display multi-format pixel data types on the display monitor, frame buffers 12, 13 and 14 provide pixel data to DAC 16 in a manner similar to a single frame buffer. In such a multi-frame buffer system, a primary frame buffer, such as frame buffer 12, supplies pixels to DAC 16. In addition to the digital to analog conversion circuitry, DAC 16 contains means for detecting a key color such as a particular color value representing a shade of blue. When DAC 16 detects the key color from the primary frame buffer 12, DAC 16 switches to an alternative pixel data stream such as YUV pixel data from frame buffer 14. Similarly, a second color key is provided to switch the pixel data stream from frame buffer 12 to frame buffer 13. Although such a multi-frame buffer system is operational, the system requires separate frame buffers for each pixel format type.
As an alternative to the multi-frame system, a single frame buffer computer graphics system, containing multi-format pixels, can be implemented. The single multi-format frame buffer comprises, in addition to the pixel data, pixel tags for each pixel. The pixels from the multi-format frame buffer are input to the DAC. The pixel tags identify the pixel format for the corresponding pixels such that each pixel is routed to an appropriate look-up table for conversion to the standard video pixel format. Although the pixel tag multi-format frame buffer requires only a single frame buffer, it requires additional memory in the single frame buffer to store the pixel tags. In addition, standard frame buffers and associated circuitry is designed to accommodate fixed pixel data lengths such as 8, 16 or 24 bits. Consequently, the pixel tag multi-format frame buffer systems require a special sized frame buffer.